Properties and Characterization of Tamarind Nut Shell Powder Filled Jute and Hemp Fibers Reinforced Hybrid Polymer Composites

The main aim of this work is to investigate the effect of hybridization and the inuence of tamarind nut shell powder (TNSP) on the properties and characterization of jute and hemp plant bers reinforced composites by varying weight % of bers. The composites are fabricated through the compression molding method and the properties such as tensile strength, tensile modulus, exural strength, exural modulus, Shore-D hardness, void content, and interlaminar shear strength (ILSS) of the hybrid composites are evaluated. The characterization studies such as Fourier transform infra-red (FT-IR) spectroscopy, water absorption behavior and scanning electron microscopy (SEM) analysis are also conducted. The results indicated that the hybrid composite samples 40:0 (jute: hemp) have the highest tensile, exural, impact strengths as well as ILSS values. The void content of 20:20 (jute:hemp) composites was reduced owing to the good adhesion and compatibility of both the bers with the matrix material.


Introduction
Composites have very good potential to replace conventional materials like steel, wood, and metallic elements due to their lightweight, high speci c strength, stiffness, availability, and economically cheap [1][2][3]. Polymer-based composites are widely utilized in several applications, including sports goods, motor boats, airplanes, missiles, space-craft, shipping, computer peripherals, naval and automotive components [4][5][6][7]. Natural bers have become increasingly common as reinforcement material for both thermosetting as well as thermoplastic polymers in recent days [8,9]. These bres are carbon neutral and can absorb the equal amount of CO 2 when they produce [10]. Moderate strength, lower density, resistance to corrosion, low thermal expansion coe cient, less energy consumption for manufacturing, and low cost for production are all advantages of polymer composites with natural ber as a reinforcement [11].
The researchers show tremendous interest in natural bers reinforcement in light of their low production costs, low equipment requirements, and high strength-to-weight ratio when compared to synthetic ber reinforcements [12]. Plant-based natural bers serve as biodegradable reinforcement materials to replace petroleum-based synthetic bers [13,14]. Pysical and mechanical properties of plant bers are largely determined by their physical structure and chemical composition, which includes ber structure, moisture content, brils angle, cellulose content, and cross-section. In a study, the volume fraction of ber shows the very good impact on both mechanical as well as physical characteristics of the composites [15]. The mechanical properties of several plant based bres reinforced composites were studied by Arputhabalan et al [16]. From the results, they found that the jute bre composites possess the maximum strength and good adhesion with polymer matrix.
Considerable amount of biological solid waste is gathered in the form land ll, garbages, etc and this causes environmental pollution. To minimize this pollution, the solid waste is coverted or modi ed into ller materials, can be mixed into polymer matrices and used for biocomposite preparation [17]. The hemicelluloses content, xyloglucon in the TNSP making it suitable ller material for bio-based composites [18]. The eco-friendly composites were fabricated by adding TNSP as nano llers for packaging applications and making of other value added products [19,20]. Few researchers have modi ed the TNSP with insitu generated copper/silver nanoparticles by thermal assisted processes and suggested this nano-llers to the preparation of antibacterial bio-nanocomposites [21,22]. TNSP/silver nanoparticles composites were prepared by using regeneration and solution casting methods [23]. The mechanical properties, FT-IR spectroscopy, XRD and SEM studies of these composites are studied and found that these composites showed good mechanical as well as actibacterial properties.
In comparison with other plant bers, both jute and hemp bers have high mechanical, physical and thermal properties [24]. Hemp and jute have many advantages, including lightweight, good tensile strength, high stiffness, recyclability, and biodegradability. Jute ber has high proportion of cellulose and hemp ber conducts heat, blocks ultra-violet rays and having anti-bacterial characteristics. Hemp ber contributes heavily towards for the load-bearing applications when reinforced with polymer matrices.
Hemp ber based polymer composites has high frictional resistance as well as low friction coe cient, which provides better wear properties [16,25]. Changing the volume of jute and hemp bers in epoxy matrix has been studied by Vimalanathan et al. [26], and found that the mechanical properties have both positive and negative effects.
The hemp/jute bres reinforced hybrid composites showed better tensile, exural, and impact strengths, as well as speci c gravity and hardness when compared with either hemp or jute ber reinforced composites [27]. Graphite ller incorporated jute and hemp bers hybrid polymer nano-composites were developed with 30°, 45° and 90° bre directions. The developed hybrid nano-composites were subjected to different mechanical loading, speci c gravity test, moisture absorption and hardness tests. It was noted that the elongation, mechanical strengths, hardness, speci c gravity are high at 90° orientation, compared to 30° and 45° orientations. Finite element modelling was done and found that the the results are highly correlated with experimental results. Hybrid hemp/kevlar and jute/kevlar based epoxy composites are developed by using hand layup technique as well as vacuum bagging process. The properties such as tensile, compression and exural strengths of these hybrid composites are studied. A relationship between the hemp/kevlar and jute/ kevlar hybrid composites has been established quantitatively. From the results it is concluded that hemp ber gave more directional properties when compared to jute and vice-versa in the transverse direction [28]. The jute-hemp bres reinforced hybrid composite materials were prepared by hand lay-up techniue and the mechanical properties of these composites are evaluated. The experimental and nite element method results of the hybrid polymer matrix composites are compared and found that they have closer values [29].
In this present experimental work, jute and hemp plant bers reinforced hybrid epoxy composites are manufactured through compression molding technique by varying weight % of bers. The properties such as tensile strength, tensile modulus, exural strength, exural modulus, hardness, void content, ILSS, FT-IR spectroscopy, water absorption behavior and SEM analysis experiments are carried out and the results are analyzed in detail.

Materials
The jute and hemp plants are harvested from Alandurai village located at the sub-urban of Coimbatore District, Tamil Nadu, India. The bers were separated from the outer part of the plant stem by means of water retting and mechanical extraction process. The tamarind nuts were taken out from the fruits, washed, dried under hot sun for 4 days and powdered. The epoxy polymeric resin (LY 556) and hardener (HY 951) are supplied by M/s. Kovai Seenu Chemicals, Coimbatore, Tamil Nadu, India.

Composite fabrication
To prepare samples for testing, the jute and hemp bers were cut into 30 cm lengths. The laminate is made up of four layers, each with jute and hemp bers alternately arranged. The TNSP is mixed with the epoxy resin was rst applied to the aluminum foil cover. The jute ber is the rst layer, followed by an epoxy resin, TNSP and hardener combination, and nally hemp ber on top of the resin. After the resin had dried, the subsequent layers were lled. Developed composites were hold for 60 min at 130°C with a pressure of 30 bar before being removed from the mold. The fabricated laminate can only be 300 x 300 x 5 mm in size (Fig. 1a).

Tensile, exural and impact tests
Computerized universal testing machine (UTM) of model ROELL Z100 was employed to perform the tensile test. The samples used had a length of 250 mm and a width of 25 mm as per ASTM D 3039 standards [30]. Experiments are carried out at a 20 cm/min crosshead speed. The exural test was performed on a same UTM following ASTM D 790 requirements [31] at a crosshead velocity of 10 mm/min. The samples used had measurements of 125 x 12.7 mm. The low velocity charpy impact test was used to examine the impact energy values of hybrid composites. The impact test samples were 60 mm x 12 mm x 5 mm in size, in accordance with ASTM D 256 standards [30]. Five samples were checked in each case for all the tests and results were recorded. The typical fractured tensile, exural and impact test specimen are shown in Fig. 1 (b-d). The experimental tensile and exural test results are given in Table 1 and the impact test results are given in Table 2.

Hardness test
Hardness is one of the essential mechanical property which is de ned as resistance to scratch or indentation. The mean hardness value (average of two indentations) of the developed composites was tested with the help of Shore D durometer. The test specimens are prepared in accordance with ASTM D 2240 standards. To obtain proper reading, the thickness of the specimen to be taken as ten times greater than the depth of the indentation [32]. The hardness results of the composite samples are given in Table   2.

Inter-laminar shear strength
Shear failure is one of the worst mode of failure in ber reinforced polymer composites. The resistance offered by the sample against shear loading is analyzed by ILSS method. This measures the strength between the layers, and provides in-plane shear modulus of the specimen [32]. Before testing, the ILSS samples are kept in the temperature around 80°C − 120°C for 5 h in a furnace and then cooled constantly at 1°C/min. A cross-head velocity of 5 mm/min was manitained during the test. The ILSS was calculated using the following Eq. (1) and the values are tabulated in Table 2.
where F = ratio of force measured and force required to de-bond, d = diameter of the sample and l = ber length embedded in the matrix.

Water absorption test
The samples were soaked in the distilled water for 120 h at room temperature and were used to measure the moisture absorption % of jute/hemp ber incorporated hybrid composites. The standard ASTM D 570 was used to prepare the test specimens [33]. After the necessary amount of time had passed, the samples were taken away from the water and rubbed with a soft cloth, and then dried for some time.
Then the samples were weighed to evaluate the water absorption behavior of composites. The water absorption of the samples is evaluated by dividing the increased weight of the specimens by the initial weight and given in Table 3.

Void content of composites
The ability to estimate the quality of composites requires knowledge of void content present in the material. The voids can be developed within composite during stacking process due to moisture content dissolved gas formation while resin ber interaction. Even though, voids are inevitable in composites, particularly those made using the compression molding technique. Voids in the composites increase the cross-sectional area which results in poor mechanical properties. The void in composites was calculated using the ASTM D 2734-94 process. The void content (V) of the developed samples was measured with theoretical and experimental densities and given in Table 4.
T d represents theoratical composite density and T d represents the experimental density.

FT-IR analysis
FT-IR spectroscopy is a method which is used to classify the chemical consitituents in the samples by passing infra-red spectra. To examine the chemical composition and constituents of jute and hemp bers, FT-IR analysis is carried out in this experiment. To achieve an infra-red spectrum, the KBr disc sample preparation method was used. Fibers are mixed with potassium permanganate in the speci ed ratio, then pelletized under vacuum condition in the mixer. Between 4000 cm − 1 and 400 cm − 1 , FTIR spectra are observed.

SEM analysis
SEM is a characterization technique used to analyze the structure of broken surfaces caused by mechanical and physical loading. The morphological representations of the developed composites are examined with aid of SEM [34]. To investigate the interfacial characteristics of developed composite and the structure of fractured surfaces, SEM analysis was performed on the composite samples. Before morphological analysis, a small portion of the sample was placed aluminum stub, in order to create conductivity silver coating was applied on the sample. The SEM micrographs were taken using standard imaging techniques.

Tensile and exural test result analysis
Jute and hemp bers hybrid composite samples were tested by appling tensile and exural loads. Table 1 presents the tensile and exural strengths as well as modulus of prepared hybrid composites of jute and hemp bers. As given in the table, the tensile strength is high (36.24 MPa) for the sample with 40 % of jute ber reinforcement. From this it is observed that, raising the proportion of jute bers in the composites shows better tensile strength as compared to other hybrid combinations. Tensile strength of only hemp ber reinforced composites is 22.43 MPa, while 10% jute and 30% hemp reinforced composites have a strength of 25.51 MPa. With a modulus of 8.960 GPa, the exural strength value of the 40% jute bers and 0% hemp ber (87.60 MPa) is found to be higher. The exural results of composites fabricated with 0% jute and 40% hemp bers were the lowest (57.11 MPa). The analysis of the tensile and exural test results are explained in Fig. 2. From the gure it is clearly noted that the strengths and modulus of these bers reinforcements are found to differ linearly by varying jute ber weight %. The hybrid composite's tensile and exural strengths were found to be higher at 40 % jute ber combination. Due to the reinforcement of jute bers in the composites the tensile as well as exural strength are increased when compared to hemp ber reinforcement. Figure 2 clearly indicates jute ber addition to epoxy matrix material increases the both strengths as well as moduli of hybrid composites.

Impact test result analysis
The analysis of energy absorbed during impact loading is presented in Fig. 3. The gure shows that the jute ber adds a lot of strength to the material, the 40:0 (jute: hemp) composites tend to have a higher impact value than other developed composites. Impact strength of the composite increases because jute ber has higher cellulose content, when compared to other plant bers. The impact energy absorbed is increased with the higher jute ber percentage because more energy is needed to break the ber/matrix bonding. The gure further reveals that the hybrid composite samples with 0% jute and 40% hemp bers exhibited low impact strength due to the porosity and spiral angle of bers.

Hardness test result analysis
The reinforcement of natural ber in the epoxy which enhances the hardness of the composites developed. Hardness results are given Table 2 and the comparisons are explained in Fig. 3. From the gure it is known that the hardness (Shore-D) of 40% jute ber reinforced composites is maximum (87.05) and 40% hemp ber reinforced composites having the lowest hardness of 73.1. This improved crack propagation which is also due to the excellent bonding between the reinforcement and epoxy resin. Due to this stress adjacent, laminate got deformed, which can lead to failure along the midplane if the gap between successive layers is large enough.

ILSS test result analysis
The ILSS of jute/hemp bers reinforced hybrid composite samples is presented in Fig. 3. From the table it is evident that the range of ILSS is in between 2.51 and 3.52 MPa. From the results it is noted that the 40:0 (jute:hemp) hybrid composite has the highest ILSS of 3.52 MPa among all hybrid composites analyzed in this study, as a result of increased jute ber volume fraction and 0:40 (jute: hemp) hybrid composites, has the minimum shear strength of 2.51 MPa. This is because of the in uence of the bonding strength at the interface of the bers and matrix. As a consequence, it's necessary to assess the ILSS using a test in which the composite laminate fails in a shear mode.

Water absorption test result analysis
Lingo-cellulosic ber's highly polar and hydrophilic nature makes it di cult to make natural berreinforced hybrids, resulting in poor bonding with the matrix material and mechanical properties were reduced due to the increased moisture content. As a result, the test was conducted for jute and hemp bers hybrid composite materials with various volume fractions and water absorption behavior were investigated, and the results are presented in Table 3. The percentage moisture absorption of the samples are calculated and the values are plotted in Fig. 3. The gures clearly denotes that the water absorption level is high in the 20% jute and 20% hemp ber hybrid composites and low in the 40% jute and 0% hemp hybrid composite samples. The water absorbance level is increased with higher hemp ber reinforcement and jute ber reinforcement in the epoxy matrix produces a lower water absorption.

SEM morphology analysis
Cracks, fractured surfaces, and ber orientation of the hybrid composite materials are observed using SEM micrographs. The SEM images of the hybrid composite specimens underwent to different types of loading are shown in Fig. 5. The micrographs display the ber fractures caused by mechanical loading (Fig. 5a-c). The surface of the samples gets roughened due to hardness, as seen in the micrograph presented in Fig. 5d. Since the ber-matrix adhesion has improved, the ber pull-out has decreased. Fiber fracture and delamination are also normal due to the ber pull out (Fig. 5e). Bad roughening of the surface may be caused by the removal of water content from the ber surface (Fig. 5f). This means that the ber and matrix are well-bonded during the interphase. Composite with improved exural strength and modulus is due to ber concentration, which provides resistance to ber fracture. The maximum strength was reported for the sample 40% of jute ber having good interfacial bonding strength, less intra ber delamination according to the ndings from SEM images.

Conclusion
The mechanical strengths, hardness, void content, ILSS and FT-IR spectra of jute and hemp bers strengthened TNSP lled hybrid composites fabricated by compression moulding process are tested experimentally. The effect of hybridization and in uence of TNSP on the physical and mechanical properties of the composites are investigated. The following conclusions are arrived from the results: The tensile strength of the 40:0 (jute:hemp) composite samples are 34.24 MPa, which is signi cantly higher than the other tested samples.
According to the results, the composites with 40% jute ber and 0% hemp ber have the highest exural strength value of 87.60 MPa.
The composites maximum impact strength as well as ILSS values are 2.35 J and 3.52 MPa for the 40:0 (jute: hemp) composite sample.
Jute/epoxy with 40:0 ratio sample shows the maximum Shore-D hardness (87.05 Shore-D) compared to other hybrid samples.
Due to the excellent interfacial bonding strength of jute bers with epoxy resin, the void content is better except 20:20 (jute: hemp) hybrid composites.
Water absorption level is also high in the 20% jute and 20% hemp ber hybrid composites and low in the 40% jute and 0% hemp hybrid composite samples.
Fiber matrix adhesion is increased, resulting in decreased ber pull out, according to SEM image analysis of the broken surfaces of the hybrid composite specimens. The typical (a) fabricated hybrid composite laminate, (b-d) fractured tensile, exural and impact test specimens  FT-IR spectrum of (a) jute and (b) hemp ber samples Figure 5